#define _CRT_SECURE_NO_WARNINGS 1
#include <cmath>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include<math.h>
#include<stdlib.h>
#include<stdio.h>
#include<unordered_map>
#include<queue>
#include<stack>
#include <functional>
#include <memory>
using namespace std;

class Solution {
public:
    int waysToStep(int n) {
        if (n == 1 || n == 2) return n;
        if (n == 3) return 4;
        vector<int> dp(n + 1, 0);
        dp[1] = 1, dp[2] = 2, dp[3] = 4;
        for (int i = 4; i <= n; i++)
            dp[i] = ((dp[i - 2] + dp[i - 1]) % 1000000007 + dp[i - 3]) % 1000000007;
        return dp[n];
    }
};

int main()
{
    vector<int> in(30, -1);
	return 0;
}